Determining the weight of a passenger or driver of a motor vehicle allows the weight of the occupant of a particular seat within a motor vehicle to be used as one variable by an airbag logic system which decides whether and how to deploy an airbag. One approach to determining the weight of a car seat occupant is to place force sensor assemblies in the load path between the seat cushion and the seat frame or other seat structure. Force sensor assemblies employing piezoelectric sensors or strain gauges are well known. However, a load sensor for use in an automobile has unique requirements. First, the loads to be measured are relatively low compared to typical force sensor assembly configurations. Second, the sensors must operate over a long period of time, as long as ten years or more, without adjustment or maintenance. The sensors must be low cost, yet must achieve high reliability and reasonable sensitivity.
Micro machined pressure sensors based on silicon are known and can readily be integrated with circuitry to monitor and calibrate a pressure sensor. Such silicon based sensors can have the necessary low cost and self-calibration and testing necessary to work over the long term and in the environmental extremes to which the interior of automobiles are subjected. Nevertheless, integrating such a sensor into a package which can be placed in the load path of a car seat and which can be used to measure occupant weight presents a difficult problem.
What is needed is a force sensor assembly for measuring the weight of an automobile occupant which is low cost, durable, and capable of self-test and calibration.